Use a direct include of strings headers in content/p*/.

content/public/browser/plugin_service.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_PLUGIN_SERVICE_H_
 #define CONTENT_PUBLIC_BROWSER_PLUGIN_SERVICE_H_
 
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "content/common/content_export.h"
 
 class GURL;
 
 namespace base {
 class FilePath;
 }
 
 namespace webkit {
 struct WebPluginInfo;
@@ skipping 119 matching lines @@
 #if defined(OS_MACOSX)
   // Called when the application is made active so that modal plugin windows can
   // be made forward too.
   virtual void AppActivated() = 0;
 #endif
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_PLUGIN_SERVICE_H_